Method and mold for producing sealing plates by injection molding and sealing plates produced accordingly

ABSTRACT

To produce sealing plates consisting of a plurality of sealing rings connected by radial webs by injection molding, wall-type guide elements are arranged obliquely to the direction of flow in the mold channel which is therefore initially largely constricted in the region of weld lines formed by the convergence of the fronts of the divided plastic melt streams, said guide elements being moved out of the mold channel during the further filling of same so that the strength is significantly improved in the region of the weld lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/482,532,filed 10 Sep. 2014, which claims priority to Austria application No. A50613/2013, filed 24 Sep. 2013, both of which are incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method and a mold for producing sealingplates of fiber-reinforced plastic by injection molding, wherein thesealing plates consist of a plurality of sealing rings connected byradial webs. In addition, the invention also relates to sealing platesproduced by such a method and/or using such a mold.

The Prior Art

Plate valves having a large number of through-holes arrangedconcentrically are used in general as the intake valves and dischargevalves of reciprocating compressors that have a large stroke volume.These through-holes are either covered by a one-piece sealing plate madeof steel or plastic or they cooperate with individual profiled rings.Although the one-piece sealing plates permit a relatively uniform loadon the sealing surfaces and stop surfaces, which are under great stressduring opening and closing as a result of the compulsory joint movementof all regions of the plate, they also have disadvantages with regard toflow deflection and the associated flow losses as a result of thesealing surfaces, the coordinated movement of which is complicated toimplement. However, valves having individual sealing rings offiber-reinforced plastic may be designed relatively easily with sealingsurfaces (as so-called profiled rings), which are positioned at an anglein the flow-through direction, which results in less deflection of theflow and thus lower flow losses. Profiled plate valves having sealingplates of the type defined above are a type of hybrid, having theadvantages of the one-piece unprofiled sealing plates (joint movement)and the advantages of the individual profiled sealing rings (efficiency,sturdiness).

Flat or profiled sealing plates made of fiber-reinforced plastic aremilled from semifinished disks according to the prior art that has beencustomary in the past and then are reground. This requires a substantialmanufacturing expense and outlay of materials, which in turn has anegative influence on costs. Such sealing plates are therefore todayfinished by injection molding in smaller quantities, i.e., all the slotsand/or through-holes in the sealing plate are mapped and modeled in themold accordingly, so that the sealing plate is already in its final formafter injection molding. To improve the imperviousness, the sealingplates may also be reground and/or re-lathed after injection molding.

Although this technology is efficient per se, it still hasdisadvantages: because of geometry of the sealing plate, the meltstreams are divided during the injection molding process and fill up thechannels that are to be filled from both sides. A weld line is formedwhen the melt fronts converge. In the case of fiber-reinforced plastics,an effect can be observed whereby no fibers pass through the weld lineand therefore there is no reinforcing effect. As a result, the strengthof the weld line hardly reaches the strength level of the base material.

The problem of inadequate weld line strength has been known for a longtime and there are various ideas for counteracting it. In addition tooptimized process management, such as injection speed, pressure profileand venting of the mold, overflow channels for blurring the weld linesare also known. In many cases, the problem is achieved by a change indesign and the weld line is shifted out of the high stress zones. Ideassuch as alignment of fibers by means of electrostatic fields are notfeasible because of the high viscosities of the plastics that are used.It would be possible theoretically to penetrate or blur the weld linesduring or after their development by means of needle shut-off valvescontrolled in a timely fashion but this could not be implementedtechnically with sealing plates having up to 60 weld lines per plate.Methods using overflow regions located outside of the weld line, with orwithout activation, are known but cannot be used because of theircomplexity and the space required.

The object of the present invention is to improve upon a method and amold of the type defined in the introduction for producing such valveplates, so that the problems described here with the resulting weldlines can at least be prevented for the most part and thus a sealingplate of the type defined in the introduction can be produced byinjection molding, so that it will not have the disadvantages, such asthose described here, of such sealing plates known in the past.

SUMMARY OF THE INVENTION

This object is achieved according to the present invention with a methodof the type defined in the introduction by the fact that in the regionof weld lines formed by the convergence of the fronts of the dividedplastic melt streams, wall-type guide elements are arranged obliquely tothe direction of flow in the mold channel, which is thus initiallylargely constricted and which deflects the fronts of the melt flowsbefore they converge, each laterally to the opposite border of the moldchannel and are moved out of the mold channel during further fillingthereof. Thus, the respective weld line in the mold channel is rotatedobliquely, so that the melt fronts approaching from both sides are eachdeflected to one side. The rate of flow here increases due to theconstriction of the cross section, and the fibers of the fiberreinforcement in the plastic are strongly oriented at the respective endof the wall-type guide element. After the melt fronts have reached thetip of the narrowing channel, a pressure begins to build up, so thatessentially the melt is only then forced into the gap beneath themovable wall-type guide element. Therefore, pressure also begins tobuild up beneath this guide element. When the respective wall-type guideelement moves upward out of the mold channel during its further filling,an oblique weld line begins to develop, such that the reinforcing fibersin the fiber-reinforced plastic also move at least partially upward onboth sides of the guide element, which is itself moving upward, andtherefore they pass through the weld line, so that these obliqueelongated weld lines are now also penetrated by reinforcing fibers ofthe respective plastic bodies connected at the weld lines. This effectcan be optimized through suitable temperature management of the melt andthe molds, so that an approx. 60% improvement can be achieved withstatic loads, and with regard to the fatigue strength, an approx. 100%improvement in the weld line strength has been demonstrated.

According to one embodiment of the method according to the invention,the plastic melt is introduced into the mold from the center of thesealing plate outward, preferably separately for each radial web, withthe guide elements being arranged exclusively in the region of thesealing rings. This results in weld lines exclusively in the region ofthe sealing rings, which are under less load than the radial webs, whichnot only must transfer forces between the rings but should also haveenough elasticity to improve the sealing behavior of the individualrings.

According to another embodiment of the invention, the movement of theguide elements out of the mold channel takes place against an externallyapplied resistance force, due to the plastic melt itself which fills upthe mold channel, such that the size of this resistance force over timecan be varied advantageously during the filling of the mold. It is thuspossible in a very simple and effective manner to influence thedevelopment of the weld line as well as the reinforcement thatultimately occurs due to the fibers of the fiber reinforcement passingthrough this weld line in the finished sealing plate.

In the region of weld lines formed by the convergence of the fronts ofthe divided plastic melt streams, the mold according to the inventionfor producing such sealing plates by the method described here haswall-type guide elements obliquely to the direction of flow of the meltstreams in the mold channel, said mold channel being thereby largelyconstricted, so that these guide elements can be moved between aninitial position, in which 1-10%, preferably 4-6%, especially 5% of themold channel is cleared, and 0-20%, preferably 5-15%, especially 10% ofthe mold channel is cleared at the bottom, and a retracted position, inwhich the end face of the guide element facing the mold channel bottomforms a seal with a surrounding mold channel wall or is slightly raisedabove it, preferably amounting to 1-10% of the thickness of the sealingplate. With these designs of wall-type guide elements and/or theirextent in relation to the surrounding mold channel walls, optimumconditions are created for deflecting and influencing the melt streamsin the region of the resulting weld lines accordingly, which results inoptimum sealing plates with the aforementioned improved strengthresults.

In a further embodiment of the mold according to the invention forproducing the sealing plates, the injection ports are situated in theregion of the center of the mold, preferably separately for each moldchannel of each radial web, and the wall-type guide elements arearranged exclusively in the mold channel of the sealing rings. Asalready mentioned, in the finished sealing plate, this results in weldlines only in the region of the sealing rings, but not in the region ofthe radial webs.

In another embodiment of the invention, the wall-type guide elements maybe designed in one piece, which facilitates the guidance of the melt.However, according to another preferred embodiment of the invention,these guide elements may also consist of a plurality of individualelements, which are arranged side by side with a slight distance betweenthem, preferably being jointly movable, which facilitates the productionof the mold in particular when the individual elements are like pinshaving a round cross section, for example.

According to another refinement of the invention, the wall-type guideelements are designed with a curvature in the circumferential directionof the sealing rings, so that in the curved mold channels of theindividual sealing rings the same constriction of the cross section onboth sides of the wall-type guide elements may be set as the goal.

In another embodiment of the invention, it is provided that thewall-type guide elements are rounded on the exterior side edges and aredesigned to be rounded or with a roof-type point on the end face, whichis turned toward the mold channel bottom. It is thus possible to have aninfluence on the flow past and/or below at the side and on the lower endface of the guide elements within a wide range, which allows a widevariety of influences on the development of formation of the weld lines.

In the context mentioned last, another advantageous embodiment of theinvention is one in which the end face of the wall-type guide elementsfacing the mold channel bottom has individual flow-through regions thatare set back with respect to the end face, which is upright in theinitial position on the mold channel bottom. This yields a preciselydefinable geometry of the initial position with a very specific freecross section for flow beneath the guide elements before they are movedout of the mold.

In a particularly preferred embodiment of the invention, the wall-typeguide elements are arranged in the mold channel at an angle of 10-35° ,preferably 15° , in deviation from the respective circumferentialtangent to the mold channel, which thus yields a constriction in thedirection of flow of the plastic melt, preferably continuously. Thus,when the melt front encounters the obstacle formed at the front by theguide elements in the mold channel, this results in optimum developmentof the effects described above.

In another embodiment of the invention, the wall-type guide elements areput under a load by means of springs and/or by hydraulic, pneumatic orelectrical actuators or a combination thereof, preferably with a loadforce that can be varied over the chronological course of the variable.This permits the desired influence on the movement of the wall-typeguide elements to yield the desired development of the weld lines in amanner that is simple but can also be controlled.

The wall-type guide elements may simply be arranged flatly or with anoblique curvature in the respective mold channel—but individual ones orall of the guide elements may be bent in a V shape apart from that—and aplurality of the above-mentioned individual elements may also beprovided in any groups, which thus permits a further influence on thedevelopment and formation of the weld lines.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below on the basisof the exemplary embodiments which are illustrated schematically in thedrawings.

FIG. 1 shows an sealing plate according to the invention, which is notprofiled here for example, shown in a perspective view,

FIG. 2 shows the enlarged detail II from FIG. 1 in a view from above,

FIG. 3 shows a schematic diagram of a shape for producing a sealingplate according to FIGS. 1 and 2,

FIGS. 4 and 5 show schematically the weld lines of the type to beadjusted in the production of a sealing plate (FIG. 4 without and FIG. 5with wall-type guide elements according to the present invention),

FIGS. 6 through 12 show various designs of wall-type guide elements foruse in methods and molds according to the present invention, and

FIGS. 13 through 17 show different arrangements of wall-type guideelements consisting of individual elements.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENTS

The sealing plate 1 shown in FIG. 1 consists of a disc-shaped member 1 awhich has a plurality of concentric, circumferentially-spaced openingslb therein to provide three sealing rings 3 connected by radial webs 2,the plate being made of fiber-reinforced plastic by injection molding.This shows the sealing side of the sealing plate which in the finishedplate valve (not shown here) cooperates with the valve seat—this is thesealing plate with a flat sealing surface, which is yet to be regroundafter injection molding to improve the imperviousness. The sealing plate1 according to FIGS. 1 and 2 has not yet been ground over, which is whysickle-shaped elevations 4 can still be recognized and their developmentand function are described in greater detail below. However, apart fromflat sealing plates according to FIGS. 1 and 2, it is also possible tomanufacture so-called profiled sealing plates according to theinvention; the individual sealing rings 3 with these profiled sealingplates are provided with a chamfer around the circumference, and thesechamfers in turn cooperate with the corresponding sealing surfaces onthe valve seat (not shown)—in this case, the radial webs 2 would beformed with a recess on the sealing side opposite these lateralchamfers.

In injection molding of the sealing plate 1 shown here, fiber-reinforcedplastic is supplied with plastic melt from the innermost ring 14 whichhas a cone gate, for example, which is not shown here but is used forsupplying melt to the mold channels for the radial webs 2. During theongoing filling of the mold, four melt streams first flow outward alongthe radial webs 2 and each is divided to the right left and to the leftat the intersections with the sealing rings 3. These divided streams ofmolten plastic thus fill up the mold channels for the sealing rings 3from both ends and converge in the central region between the radialwebs 2. In the absence of the wall-type guide elements 5 according tothe invention (see FIG. 3 and FIGS. 6 through 17), weld lines 15essentially like those in FIG. 4 would be obtained in the region of theconvergence of the fronts of the two melt streams, but this would resultin a reduced strength of the sealing plate 1 in this region, inparticular in a case of fiber-reinforced plastic melts, because thefibers of the fiber reinforcement of the two converging melt streamswould not pass through the weld line 15 and therefore would not provideany reinforcement there.

Therefore, in the method according to the present invention, a wall-typeguide element 5 is arranged obliquely to the direction of flow in themold channel 6 which is therefore initially largely constricted, asrepresented schematically in FIG. 3, in the region of the weld lines 15formed by the convergence of the fronts of the divided plastic meltstreams. These guide elements 5 are moved out of the mold channel 6during the further filling of same (toward the top in FIG. 3), namelybeing moved out of the initial position depicted in FIG. 3 into aretracted position, in which the bottom side near the mold wall forms aseal with the surrounding mold channel wall or is raised slightly abovesame. Raising the guide elements slightly above the surrounding moldchannel wall causes the elevations 4 to be formed, as depicted in FIGS.1 and 2, which are then removed in regrinding the sealing plate 1.

According to FIG. 3, the movement of the guide elements 5 may take placeeither simply by means of the pressure occurring between mold channelbottom and the guide element 5 in the continued filling in the plasticfeed (against the force of a spring 7) or by means of an actuator A, forexample, an electric actuator, or by means of a pneumatic or hydrauliccylinder 8 or a combination thereof, such that the chronological courseof the movement or of the acting opposing pressure can also becontrolled here in a manner which is not depicted further.

It can be seen clearly from FIG. 2 that with the mold used for thissealing plate 1, the wall-type guide elements 5 are curved in thecircumferential direction of the sealing rings 3 and have rounded areason the outer side edges. The angle a formed by the wall-type guideelements 5 with the circumferential tangent 9 of the sealing rings 3and/or of the corresponding mold channel is preferably in the range of10-35° with which the melt streams striking the guide elements 5 fromboth sides are deflected accordingly, such that the elevated pressuredue to the constriction of the mold channel to an equal extent on bothends is also built up beneath the guide elements 5, tending to displacethem upward out of the mold channel in the course of further filling.This yields a strong alignment of the fibers of the fiber reinforcementin the plastic melt along the guide elements 5 moving upward out of themold, which results in the desired inclined position of the weld line 15(see FIG. 5) with simultaneous penetration of same with fibers of thefiber reinforcement from both melt streams. In the initial position ofthe wall-type guide elements 5 depicted in FIG. 3, approx. 5% of themold channel is preferably cleared on both sides and approximately 10%is cleared at the bottom, which yields a very advantageous design of theweld line 15 with excellent strength values for the sealing plate 1.

Various possibilities for advantageous design of the end faces 10 of thewall-type guide elements 5 are illustrated in FIGS. 6 through 12, suchthat the term “end face 10” is to be understood to refer to the bottomside of the guide elements 5 facing the mold channel bottom according toFIG. 3, said bottom side constricting the mold channel at the bottom inthe initial position. The end face 10 is designed to be straight in FIG.6 (as also indicated in FIG. 3). According to FIG. 7, the end face 10 isprovided with a rounded area over the entire length. FIG. 8 shows aninclination at the center, such that the edge regions are not inclinedand therefore the guide element 5 can be set in the initial position onthe mold bottom. FIGS. 9 and 10 show rooftop-shaped slopes of the endface 10, such that in the embodiment according to FIG. 10, the firstedge of this inclined surface runs from one side of the guide element tothe other, which has a targeted influence on the flow beneath the guideelements 5 and thus has a targeted influence on the design of theresulting weld line. The discussion according to FIGS. 11 and 12includes flow-through regions 11 and exterior regions 12 standingupright on the mold channel bottom in the initial position.

However, apart from the design of the wall-type guide elements 5according to FIG. 3 and FIGS. 6 through 12 as one-piece parts, theseguide elements 5 according to FIGS. 13 through 17 could also consist ofa plurality of individual elements, labeled as 13 here, that arearranged side by side with a small distance between them and arepreferably jointly movable. According to FIGS. 13 through 16, pinshaving a round cross section are used — the cross section of theseindividual elements 13 is oval according to FIG. 17. This also resultsin a wide variety of possibilities for influencing the melt streams inthe region of the resulting weld lines. In addition, weld lines can beproduced with the guide elements 5 according to FIGS. 6 through 12, aswell as with those according to FIGS. 13 through 17; in deviation fromFIG. 5, it is possible to manufacture these guide elements not only tostand essentially obliquely, but also to have V-shaped or similargeometries, which can likewise contribute toward an improvement in thequality of the resulting sealing plates 1.

What is claimed is:
 1. A mold for production of sealing plates whichconsist of a plurality of sealing rings connected by radial webs, madeof fiber-reinforced plastic by injection molding, wherein wall-typeguide elements are arranged obliquely to the direction of flow of themelt streams in the mold channel, which is thereby largely constrictedin the region of weld lines formed by the convergence of the fronts ofthe divided plastic melt streams, these guide elements being movablebetween an initial position, in which 1-10%, preferably 4-6%, especially5% of the mold channel is cleared on both sides and on the bottom 0-20%,preferably 5-15%, especially 10% of the mold channel is cleared at thebottom, and a retraction position in which the end face of the guideelement facing the bottom of the mold channel forms a seal with thesurrounding mold channel wall or is elevated slightly above it,preferably amounting to 1-10% of the thickness of the sealing plate. 2.The mold according to claim 1, wherein the injection ports are arrangedin the region of the center of the mold, preferably separately for themold channel of each radial web, and the wall-type guide elements arearranged exclusively in the mold channels of the sealing rings.
 3. Themold according to claim 2, wherein the wall-type guide elements aredesigned in one piece.
 4. The mold according to claim 2, wherein thewall-type guide elements consist of a plurality of individual elementsthat are arranged side by side with a slight distance between them,preferably being jointly movable.
 5. The mold according to claim 3,wherein the wall-type guide elements are curved in the circumferentialdirection of the sealing rings.
 6. The mold according to claim 5,wherein the wall-type guide elements are rounded on the outer side edgesand are rounded on the end face facing the bottom of the mold channel orthey are designed with a point like a rooftop.
 7. The mold according toclaim 6, wherein the end face of the wall-type guide elements, saidfaces turned toward the bottom of the mold channel, has individualflow-through regions that are set back with respect to the end facesitting on the bottom of the mold channel in the initial position. 8.The mold according to claim 7, wherein the wall-type guide elements arearranged at an angle of 10-35° , preferably 15° , in deviation from therespective circumferential tangent to the mold channel, so as to form apreferably continuous constriction in the direction of flow of theplastic melt.
 9. The mold according to claim 8, wherein the wall-typeguide elements are put under a load by means of springs and/or withhydraulic, pneumatic or electric actuators, or a combination thereof,preferably with a load force that can be varied in the curve of thevariable over time.
 10. The mold according to claim 9, wherein thewall-type guide elements form a V-shaped angle.